Various methods for producing carbon nanotubes have been developed, notably by chemical vapour deposition (CVD) and electric arc discharge. In the CVD method, a carbon containing gas is catalytically converted by a metal catalyst into carbon nanotubes and other carbon nanostructures. In the electric arc method, a direct current (DC) electric discharge is generated between a pair of graphite electrodes which evaporates carbon from the electrode surfaces.
The electric arc process is non-continuous since it must be stopped to replace the carbon electrodes after they are consumed. CVD processes are also typically non-continuous processes, relying on surface deposition and growth of the carbon nanotubes, and also suffer from the drawback that single-walled carbon nanotubes are much more difficult to produce than multi-walled carbon nanotubes.
Recent work described in WO 03/095362 describes a method for continuously producing single walled carbon nanotubes in a plasma torch in which a secondary plasma is formed by contacting a carbon-containing substance with a primary plasma formed at the plasma discharging end of the plasma torch. While the carbon containing substance is described to include solid carbon as well as liquid or gaseous sources, the latter is preferred and the supporting example of a carbon-containing substance is ethylene gas. It is submitted that such apparatus does not attain sufficiently high temperatures in the primary or secondary plasma to vaporize solid phase carbon and/or catalyst sources. The sole usage of solid precursors described in WO 03/095362 is a low vapour pressure organometallic compound which is vaporized prior to the plasma and delivered to the plasma in a gaseous phase.
An object of this invention is to provide a reactor and process for the continuous production of high purity single-walled carbon nanotubes.